1. Field of the Invention
The invention relates to a method of distillation, especially of ethanol from a mash.
2. Description of the Related Art
In a conventional method of distillation and dehydration of ethanol from a beer mash, which contains about 10% ethanol, 85% water, and 5% solids, the mash is preheated and fed into a first distillation column. In the first distillation column, the mash is concentrated by evaporation, and the solids are removed as a bottom product together with water. A portion of the bottom product is usually returned to the distillation column after heating (reboiler).
The first distillate in the form of a vapor, which still contains water, ethanol, and fusel oils, is fed, possibly via a collecting and mixing tank, into a second distillation column, which is designed as a rectifying column. A more extensive separation is carried out in this rectifying column, and the fusel oils are removed in a sidestream. Of the water separated as bottom product in the second distillation column, a small fraction is returned to the rectifying column after heating (reboiler), and the remainder is removed, so that it is eliminated from the production process. The distillate of the second distillation column, which, as before, contains water and ethanol, can be partly returned to the first and second distillation columns, possibly via the aforementioned collecting tank.
Most of the ethanol/water mixture that constitutes the second distillate and contains about 95% ethanol and 5% water is subjected to a final dehydration, which yields ethanol that is as pure as possible with a purity of 99 to 99.8%. This last dehydration is carried out with molecular sieves, in which crystalline zeolites adsorb H2O molecules like a sponge.
However, the zeolites of a molecular sieve quickly become saturated with water. Therefore, the water-saturated zeolites must be regenerated to achieve constant dehydration. Consequently, molecular sieves are usually used in pairs. Highly pure ethanol can then be made available by a first, active molecular sieve, and this ethanol can also be used for regenerating a second, passive molecular sieve. In the regeneration of a passive molecular sieve, the ethanol used for this purpose can be returned to a distillation column, and this return flow can amount to about 30% of the pure ethanol obtained from the active molecular sieve. In this process, the constant change of the pressure load of the molecular sieves causes dust-like abrasion of the filler material. This loads downstream stages of the installation, which must be completely replaced on a periodic basis. This has unfavorable consequences for capital expenditures and operating costs.
The dehydration of ethanol is an energy-intensive process. Especially the concentration of the mash by evaporation in the first distillation column and the necessity of large amounts of distillate reflux result in considerable operating costs and capital expenditures. In addition, it is necessary to achieve a high degree of purity of the ethanol/water mixture of about 90-95% before a treatment with molecular sieves can be carried out, so that the mixture of substances must be rectified to bring it as close as possible to the azeotropic point, which results in very high equipment expense and operating costs. Consequently, a large number of separating stages and a high level of reflux are necessary in the rectifying column.